That brings us to evaluate CO2, a supposedly “natural” refrigerant that, despite having low GWP, falls short on several other factors that are important to supermarkets:
Switching to CO2 can be disruptive and costly. It requires entirely new equipment because CO2 -based systems function at high pressures, and as a result, need costly components that must withstand high pressure conditions.
When a leak occurs in a CO2 system, it is very rapid due to the high pressures of CO2 . Furthermore, there is no recovery equipment for CO2, meaning repairs often lead to complete system discharge.
Unlike HFO-based systems, CO2-based systems are complex and difficult to repair, and demand specialized skills and capabilities. This makes finding qualified technicians a real challenge. There are also concerns regarding whether a refrigeration system running at such a high pressure will have as long a lifespan as a traditional system.
CO2 has significant short-term supply and pricing challenges. As the fossil fuel-based economy winds down, it is anticipated that less CO2 will be available as a byproduct of these industrial processes, thus creating the need to produce CO2 refrigerant “on purpose.” This will impact the supply and significantly drive up the production cost of refrigerant-grade CO2 .
More than 95% of a typical supermarket’s lifetime greenhouse gas (GHG) emissions are generated through the system's energy consumption (scope 2 emissions), according to a lifecycle comparison of CO2 refrigerants versus low GWP HFO-based refrigerants. Meanwhile, the emissions from refrigerant leaks (scope 1 emissions) have a significantly lower contribution of less than 5%.1 Because commercial refrigeration CO2 systems are less thermodynamically efficient, they consume 20% more energy than HFO-based systems, which dominate the overall lifecycle GHG impact.
Stores using higher-pressure CO2-based systems must take precautions to ensure they can survive a power outage. During a power outage, refrigeration systems warm to ambient conditions. This requires a backup generator and an HFO/HFC refrigeration unit or an entire system's worth of CO2 refrigerant onsite. In case of delay in managing the leak, the entire system may be down for extended periods, resulting in a loss of food safety and/or quality.
Is CO2 A "Natural Refrigerant? You Decide.
Contrary to what the word natural implies, CO2 is not captured out of the air, but is instead produced in large industrial plants, where it is captured as a fossil fuel byproduct and must undergo additional refining to achieve a refrigerant-grade standard.
It's time to reassess CO2-based systems and consider a transition to low GWP refrigerants such as Solstice® HFO and HFO blends.
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1Based on Honeywell eco-efficiency simulation for 20 year period
2Technology Options for Low Environmental Impact Air-Conditioning and Refrigeration Systems, ORNL/TM- 2023/3041, Pub200582.pdf (ornl.gov